[PATCH v1 2/2] ufs: rpmb: use a fixed-length RPMB dev_id

[Jorge Ramirez-Ortiz]

The RPMB authentication key is derived from the dev_id handed to the
RPMB subsystem. OP-TEE implements the eMMC RPMB flow, where the dev_id
is the eMMC CID, a fixed 16-byte value, and it derives the key on that
assumption.

The UFS RPMB id built here is "<device_id>-R<region>", which is variable
length and longer than 16 bytes. Passing it verbatim would tie the
derived key to a length OP-TEE does not expect and diverge from the
fixed-CID eMMC ABI, requiring OP-TEE to be taught about variable-length
UFS ids.

Hash the UFS id into a fixed 16-byte dev_id with blake2s instead. This
keeps the derived key stable and unique per region while matching the
eMMC CID layout OP-TEE relies on, so the key-derivation ABI stays
identical and no OP-TEE change is needed.

Signed-off-by: Jorge Ramirez-Ortiz <jorge.ramirez@xxxxxxxxxxxxxxxx>
---
 drivers/ufs/core/ufs-rpmb.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/drivers/ufs/core/ufs-rpmb.c b/drivers/ufs/core/ufs-rpmb.c
index d0c7ea7a36f4..b800871269bb 100644
--- a/drivers/ufs/core/ufs-rpmb.c
+++ b/drivers/ufs/core/ufs-rpmb.c
@@ -10,6 +10,7 @@
  *	Can Guo <can.guo@xxxxxxxxxxxxxxxx>
  */
 
+#include <crypto/blake2s.h>
 #include <linux/module.h>
 #include <linux/device.h>
 #include <linux/kernel.h>
@@ -21,6 +22,7 @@
 #include <linux/unaligned.h>
 #include "ufshcd-priv.h"
 
+#define UFS_RPMB_ID_LEN			16	/* Match eMMC CID Length */
 #define UFS_RPMB_SEC_PROTOCOL		0xEC	/* JEDEC UFS application */
 #define UFS_RPMB_SEC_PROTOCOL_ID	0x01	/* JEDEC UFS RPMB protocol ID, CDB byte3 */
 
@@ -154,6 +156,7 @@ int ufs_rpmb_probe(struct ufs_hba *hba)
 {
 	struct ufs_rpmb_dev *ufs_rpmb, *it, *tmp;
 	struct rpmb_dev *rdev;
+	char *dev_id = NULL;
 	char *cid = NULL;
 	int region;
 	u32 cap;
@@ -213,8 +216,17 @@ int ufs_rpmb_probe(struct ufs_hba *hba)
 			goto err_out;
 		}
 
-		descr.dev_id = cid;
-		descr.dev_id_len = strlen(cid);
+		dev_id = kzalloc(UFS_RPMB_ID_LEN, GFP_KERNEL);
+		if (!dev_id) {
+			device_unregister(&ufs_rpmb->dev);
+			ret = -ENOMEM;
+			goto err_out;
+		}
+
+		blake2s(NULL, 0, cid, strlen(cid), dev_id, UFS_RPMB_ID_LEN);
+
+		descr.dev_id = dev_id;
+		descr.dev_id_len = UFS_RPMB_ID_LEN;
 		descr.capacity = cap;
 
 		/* Register RPMB device */
@@ -228,6 +240,8 @@ int ufs_rpmb_probe(struct ufs_hba *hba)
 
 		kfree(cid);
 		cid = NULL;
+		kfree(dev_id);
+		dev_id = NULL;
 
 		ufs_rpmb->rdev = rdev;
 		ufs_rpmb->region_id = region;
@@ -240,6 +254,7 @@ int ufs_rpmb_probe(struct ufs_hba *hba)
 	return 0;
 err_out:
 	kfree(cid);
+	kfree(dev_id);
 	list_for_each_entry_safe(it, tmp, &hba->rpmbs, node) {
 		list_del(&it->node);
 		device_unregister(&it->dev);
-- 
2.54.0